Green-synthesized silver nanoparticles as an effective tool for promoting tobacco (Nicotiana tabacum L.) growth and development

Tobacco ( Nicotiana tabacum L.) is a model plant and significant cash crop in agriculture. However, it is exposed to a variety of biotic and abiotic stressors, which not only affect its growth and development but also reduce its yield and quality. In this work, tobacco extract served as a reductant for the successful green synthesis of silver nanoparticles (TE/AgNPs). Using seed medium and pot-based cultivation experiments, the effects of TE/AgNPs on tobacco growth were investigated. The results of growth and physiological measurements showed that TE/AgNPs significantly promoted tobacco growth. The molecular mechanisms by which TE/AgNPs promote tobacco growth were explored in depth by combining multi-omics techniques, such as transcriptomics, metabolomics, and microbiomics. Metabolomic analysis revealed that TE/AgNPs treatment induced a reprogramming of the plant metabolome, thereby modulating cellular metabolism and responses to external signaling molecules. These alterations primarily involved changes in organic acids, energy production, and secondary metabolites. Microbiome profiling demonstrated that TE/AgNPs treatment significantly altered the community structure of both root and soil microbiota, leading to the structure of microflora tended to be complex after treatment, and the "network hub" nodes of each ecological niche changed significantly. Transcriptomic analysis identified the carotenoid biosynthesis pathway as enriched among differentially expressed genes in both roots and leaves. Integrated metabolomic and transcriptomic analyses further highlighted the alanine, aspartate and glutamate metabolic pathway, as well as glutathione metabolic pathway, as playing critical roles in TE/AgNPs-promoted tobacco growth. In addition, Spearman correlation analysis was utilized to ascertain the relationship between the root differential metabolites and the "network hub" of the microbiome genus level co-occurrence network, and a total of 20 strongly correlated pairs were obtained. The molecular docking of the above strongly correlated pairs preliminarily proved the potential regulatory relationship between metabolites and microorganisms. Then, based on MetOrigin, the root differential metabolites were traced, and the results showed that metabolites Glycine, Cadaverine, Alanine and γ-Aminobutanoic acid are closely related to plant growth-promoting rhizobacteria (PGPR) such as Sphingobium, Sphingopyxis and Caulobacter. In conclusion, TE/AgNPs exerts its growth-promoting effects by regulating gene expression, metabolic pathways, and the inter-root microbial community in plants. This work presents new ideas and practical guidance for the adoption of sustainable and environmentally friendly agricultural production methods, as well as a theoretical foundation for the use of green-synthesized nanosilver as a plant growth regulator. • In this study, for the first time, silver nanoparticles with high compatibility and stability were successfully prepared by a green synthesis method using tobacco extract, providing a new method for the green synthesis of silver nanoparticles. • In this study, green synthetic nanosilver was applied to the development and cultivation of Nicotiana tabacum L. which provides a new technological solution for the sustainable use of resources and the green transformation. • Using tobacco as a model plant, this study innovatively combined multi-omics technologies to systematically analyse the molecular mechanism of green synthetic nano-silver to promote plant growth through the study of metabolites, changes in gene expression and the structure of microbial communities, and providing favourable support for the development of green nano-materials in agricultural production.